A hydraulic control for an automatic automobile transmission is known from DE 102 49 341 A1 which guarantees a drive free from breakdowns and is also cost effective to manufacture. It is suggested that instead of the known and expensive mechanical pressure reduction valves, a synchronized electromagnetic shifting valve could be used. This shifting valve matches the pressure level of the main pressure line to the control pressure level of the pressurized medium like a piston-cylinder arrangement.
A shifting unit for an automatic automobile transmission is known from the unpublished DE 102004006683 A1 which has multiple valves which are connected to each other through a pressure supply line and a pressure reduction line. Thereby the chambers of the servo cylinders which are provided with servo actuators have at least one shifting valve each. The servo cylinders which are built as piston-cylinder units have additional valves arranged so that they close separately, open and block the pressure supply and pressure reduction lines whereby the function of the pressure supply lines and the pressure reduction lines could be interchanged with the help of this shifting unit.
The objective of the invention is to develop a hydraulic or a pneumatic control for an automatic automobile transmission which has improved shifting dynamics and is also fail safe and cost effective to manufacture.
The above problem has been solved through the shifting unit for an automatic transmission with a pressurized medium control for a vehicle, with multiple valves which are connected to each other through a pressure supply line and a pressure reduction line, whereby the chambers of the servo cylinders provided with servo actuators have at least one shifting valve each and there is pressure accumulator capacity between the pressure supply line and the shifting valve.
This construction has the advantage that through the inclusion of a pressure accumulator capacity, a high dynamic of the entire system is guaranteed at all times. By designing the pressure accumulator capacity sufficiently large in comparison with the volume of the chambers in the servo cylinders, even in the case a shift is carried out, sufficiently large pneumatic or hydraulic pressure is generated very quickly. Therefore shorter shifting times can be achieved.
Advantageously in several parts of the shifting unit, preferably at the main cut off valve, a smaller and cost effective shifting element could be used.
It is of further advantage that the risk of failure is decreased further since in the case of sufficient size of the pressure accumulator capacity, it could be used for emergency switching off in the case of loss of pressure in the vehicle by keeping the main cut off valve closed.
The pressure accumulator capacity in the invention also offers other advantages. The pressure accumulator capacity could contain excess pressure irrespective of whether or not shifting is carried out at that moment or not. As a result, the dynamics of the shifting device are further increased and also prevention of an over load caused by reduction in pressure in the shifting is ensured.
The pressure reservoir can be held right even after the shift off of the vehicle fitted with a shifting unit which is good for the starting process with reference to control and regulation mechanisms while starting the vehicle again.
By having a large enough pressure accumulator capacity, it can initiate emergency switching off in the case of loss of pressure in the vehicle due to closure of the main shifting valve.